Solenoid

ABSTRACT

A solenoid that has a small body and increased propulsion in a controlled range is provided.  
     The solenoid is characterized by being provided with a bearing  40  formed of a nonmagnetic body, n (where n is a positive integer of zero or above) grooves  56  and n+1 tooth parts  58  that are adjacent to the grooves  56  and function as magnetic poles being provided in a facing surface  52  of a first upper yoke  54   a , m (where m is a positive integer of zero or above) grooves  70  and m+ 1  tooth parts  72, 74  that are adjacent to the grooves  70  and function as magnetic poles being provided in a facing surface  55  of a second upper yoke  54   b , n+1 grooves 56 and n+1 tooth parts  58, 59  that are adjacent to the grooves  56  and function as magnetic poles being provided in a surface  52  of the slider  36  that faces the first upper yoke  54   a , and m grooves  76  and m tooth parts  78  that are adjacent to the grooves  76  and function as magnetic poles being provided in a surface  55  of the slider  36  that faces the second upper yoke  54   b.

TECHNICAL FIELD

The present invention relates to a solenoid used as an actuator.

BACKGROUND ART

FIGS. 5 and 6 show constructions of typical solenoids that areconventionally known.

A solenoid 10 includes an excitation coil 12, a yoke 14 that isassembled so as to surround the excitation coil 12, a bearing 15disposed in a central part of the excitation coil 12, and a slider 16 (amoving iron core or plunger) that is guided in a sliding state by thebearing 15 (see FIGS. 1 and 2, etc., of Japanese Laid-Open PatentPublication No. H05-211744).

The yoke 14 is constructed of at least two members, an upper yoke 14 aand a lower yoke 14 b, with the upper yoke 14 a being disposed at oneend and the lower yoke 14 b being provided so as to close the other endof an enclosure 19 for the slider 16 so as to limit the movement in adirection A of the slider 16.

A surface 14 c of the lower yoke 14 b facing the other end-end surface16 a of the slider 16 functions as a fixed iron core.

When current flows through the excitation coil 12 of the solenoid 10shown in FIG. 5, a magnetic path a is formed as shown by the dashedline, for example. It should be noted that the direction of the magneticpath a shown here is merely an example.

The magnetic path a passes inside the yoke 14, enters into the slider 16from the upper yoke 14 a, moves through the slider 16 along the axialdirection toward the lower yoke 14 b side, and passes to the fixed ironcore part 14 c of the lower yoke 14 b from the other end-end surface 16a of the slider 16 via the air. Then the magnetic path a passes from thelower yoke 14 b to the upper yoke 14 a so as to form a closed loop.

The slider 16 is pulled onto the fixed iron core part 14 c by themagnetic force produced in the gap B between the other end-end surface16 a of the slider 16 and the fixed iron core part 14 c of the loweryoke. This magnetic force is the propulsion of the solenoid.

The propulsion of the solenoid 10 decreases exponentially in accordancewith the distance of the gap B (that is, the stroke).

The construction of another conventional solenoid is shown in FIG. 6.Here, components that are the same as in the construction of thesolenoid shown in FIG. 5 have been assigned the same reference numeralsand description thereof has been omitted.

In this solenoid 20 also, the lower yoke 14 b is provided so as to coverthe other end-side end of the enclosure 19 for the slider 16. The fixediron core part 14 c of the lower yoke 14 b is provided so as to protrudeinto the enclosure 19 for the slider 16, and a front end of the fixediron core part 14 c is formed as a concave 17 that is hollow inaccordance with the shape of the other end-end surface 16 a of theslider 16.

The other end-end surface 16 a of the slider 16 is formed with asharpened front end where the radius gradually decreases toward theother end-side so as to be capable of being enclosed in the concave 17formed in the front end of the fixed iron core part 14 c (see FIG. 1 ofJapanese Laid-Open Patent Publication No. H07-336943).

The magnetic path in this solenoid 20 forms the same route as themagnetic path of the solenoid 10 shown in FIG. 5, and therefore is notillustrated, with the propulsion of the solenoid 20 being generated by agap between the fixed iron core part 14 c and the other end-end surface16 a of the slider 16. It is also known that the propulsion-displacementcharacteristics change in accordance with the taper angle of the otherend-end surface 16 a of the slider 16 in the solenoid 20.

As described above, the propulsion of the solenoid is determined by themagnitude of the magnetic energy stored in the gap between the fixediron core and the slider. That is, magnitude of the propulsion isdetermined by the distance between the fixed iron core and the slider.

Here, the relationship between the stroke (amount of displacement) ofthe slider and the generated propulsion in a conventional solenoid isshown in FIG. 7. As shown in FIG. 7, in a conventional solenoid, thepropulsion is smallest at a position where the slider is furthest awayfrom the fixed iron core part and the propulsion increases as the sliderapproaches the fixed iron core part.

However, when the movable range of the slider and the controlled range(the operation range) have the relationship shown in FIG. 7, it is notpossible to use large propulsion within the controlled range throughwhich control of the solenoid is actually desired. The propulsioncharacteristics are also nonlinear, which means the controllability ispoor.

In this kind of conventional solenoid, propulsion is generated betweenend surfaces of the slider at the end of the movable range and the fixediron core part, and there has been the problem that as the movable rangebecomes wider, it has not been possible to set the controlled range atthe optimal range in the propulsion characteristics of the solenoid.

There has also been the problem that in cases where the movable range iswide and the required propulsion in the controlled range is large, thesize of the solenoid itself has to be increased to produce thepropulsion.

For this reason, to solve the above problems, it is an object of thepresent invention to provide a solenoid that is small and where thepropulsion within the controlled range can be increased.

DISCLOSURE OF THE INVENTION

That is, a solenoid according to the present invention includes: anexcitation coil; a slider disposed in a center part of the excitationcoil; and a yoke including a first yoke part that covers one end surfaceof the excitation coil and has a facing surface that faces an outercircumferential surface of the slider, a second yoke part that coversanother end surface of the excitation coil and has a facing surface thatfaces the outer circumferential surface of the slider, and a linkingpart that links the first yoke and the second yoke and covers an outercircumferential part of the coil, the yoke forming a closed magneticpath together with the slider, wherein a non-magnetic bearing issandwiched between the facing surface of the first yoke part and thefacing surface of the second yoke part, is disposed on an outercircumference of the slider, and guides the slider in a movable state, n(where n is a positive integer of 0 or higher) grooves, which areprovided so as to be concave around an inner circumference, and n+1tooth parts, which are adjacent to the grooves and function as magneticpoles, are provided in the facing surface of the first yoke part, m(where m is a positive integer of 0 or higher) grooves, which areprovided so as to be concave around an inner circumference, and m+1tooth parts, which are adjacent to the grooves and function as magneticpoles, are provided in the facing surface of the second yoke part, n+1grooves, which are provided so as to be concave around an outercircumference, and n+1 tooth parts, which are adjacent to the groovesand function as magnetic poles, are provided in a surface of the sliderthat faces the first yoke part, and m grooves that are provided so as tobe concave around an outer circumference and m tooth parts that areadjacent to the grooves and function as magnetic poles are provided in asurface of the slider that faces the second yoke part.

The effects of the above construction are as follows.

That is, a magnetic path is formed inside the slider via the first yokepart and the second yoke part that face an outer circumferential surfaceof the slider and since unlike the conventional art, the propulsiongenerated between end surfaces of the slider and of a fixed iron corepart is not required, the body size of the solenoid can be made smallerthan before.

In addition, a portion of a fixed iron core part facing the end surfaceof the slider is not required to generate propulsion, therefore themovement of the slider is not limited with respect to the direction ofmovement. This means that regardless of the distance of the actualmovable range of the slider, the solenoid can be designed so that anoptimal range in the propulsion characteristics is used as thecontrolled range.

In addition, since propulsion is generated at two portions that are thefirst yoke part and the second yoke part, even when the stroke graduallyapproaches zero, the region where the propulsion is stable can bewidened and the control characteristics can be improved without thepropulsion increasing exponentially as in the conventional art.

Here, even if a facing surface were provided on the yoke as a magneticpole, the magnetic path between the yolk and the slider formed in adirection perpendicular to the outer circumferential surface of theslider would contribute almost nothing to the propulsion without grooveson the surface of the slider (that is, if there were no tooth partsformed as magnetic poles). It should be noted that since it is knownthat propulsion is proportional to dP/dx (where P is permeance (thereciprocal of magnetic reluctance) and x is the displacement of theslider), to obtain propulsion, it is necessary to provide a constructionwhere the permeance changes in accordance with the movement of theslider. For this reason, the invention obtains propulsion by providing agroove or grooves in the slider so that the permeance changes inaccordance with the movement of the slider.

In addition, by assembling the first yoke part and the second yoke partwith the bearing as an alignment, the respective gaps between the sliderand the facing surface of the first yoke part and the facing surface ofthe second yoke part can be made extremely small with high precision.This means that the efficiency of the conversion from the electricalenergy supplied to the excitation coil to magnetic energy is increased,and higher propulsion can be obtained.

By forming the facing surfaces on the first yoke part and the secondyoke part with the same internal diameter, as described above, theefficiency of the conversion from the electrical energy supplied to theexcitation coil to magnetic energy is increased, so that higherpropulsion can be obtained.

The grooves and the tooth parts may be formed so as to be rectangular ortrapezoidal in cross-section.

It should be noted that a part, which is an upper end edge part of thegroove provided in the slider and is located on a far side with respectto the bearing in an axial direction, may be formed at a position thatdoes not contact the bearing in a range where the slider moves.

With this construction, the upper end edge part of the groove isprevented from contacting and thereby damaging the bearing. This meansthat the working life of the solenoid can be extended.

In addition, if a recess is formed at the entrance of the bearing sothat a part, which is an upper end edge part of the groove provided inthe slider and is located on a far side with respect to the bearing inan axial direction, does not contact the bearing in a range where theslider moves, the upper end edge part of the groove can be preventedfrom contacting and thereby damaging the bearing. This means that theworking life of the solenoid can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a first embodiment of asolenoid according to the present invention when viewed from a sidesurface,

FIG. 2 is a cross-sectional view showing a second embodiment of asolenoid according to the present invention when viewed from a sidesurface,

FIG. 3 is a cross-sectional view showing a third embodiment of asolenoid according to the present invention when viewed from a sidesurface,

FIG. 4 is a graph showing the propulsion-displacement characteristics ofa solenoid according to the second embodiment,

FIG. 5 is a cross-sectional view showing a conventional solenoid whenviewed from a side surface,

FIG. 6 is a cross-sectional view showing a different conventionalsolenoid when viewed from a side surface, and

FIG. 7 is a graph showing the propulsion-displacement characteristics ofa conventional solenoid.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to the attached drawings.

First Embodiment

In the present embodiment, the parameters n, m given in the patentclaims are set so that n=0 and m=0. The present embodiment will bedescribed with reference to FIG. 1.

A solenoid 30 includes an excitation coil 32, a yoke 34, and a slider36.

The excitation coil 32 is formed in a tube shape by winding a coilaround a bobbin 31. An enclosure 33 in which a slider 36 can be enclosedis formed at the center of the tube-shaped excitation coil 32.

The yoke 34 is made of a magnetic material, and is formed so as to covera periphery of the excitation coil 32. The yoke 34 is composed of anupper yoke 34 a disposed at one end of the excitation coil 32 and alower yoke 34 b disposed at the other end.

It should be noted that the “first yoke part” referred to in the patentclaims corresponds to the upper yoke 34 a and the “second yoke part” tothe lower yoke 34 b. It should be noted that the “linking part” referredto in the patent claims also corresponds to the lower yoke 34 b of thepresent embodiment and is constructed so as to be integrated with thesecond yoke part.

The slider 36 is a member composed of a magnetic body and is disposedinside the enclosure 33 in the central part of the excitation coil 32.The slider 36 operates in the direction of an attractive force due tomagnetic energy produced by the excitation coil 32.

It should be noted that movement in the protruding direction of theslider 36 is caused by a spring or the like (not shown).

A bearing 40 is disposed on an inner wall of the enclosure 33 formed inthe central part of the excitation coil 32 so as to surround an outercircumferential surface of the slider 36. The bearing 40 is composed ofa nonmagnetic body. The bearing 40 is sandwiched at both ends in theaxial direction by the upper yoke 34 a and the lower yoke 34 b.

It should be noted that a cover 37 is provided on the lower yoke 34 b soas to cover an open end on the other end-side of the enclosure 33.

An inner wall surface of the upper yoke 34 a that protrudes into theenclosure 33 is a facing surface 42. The facing surface 42 is disposedfacing the outer circumferential surface of the slider 36 and isdisposed so as to become a magnetic pole for the outer circumferentialsurface 36 b and the end surface 36 a of the slider 36.

That is, in the present embodiment, the facing surface 42 is a “toothpart”.

The facing surface 42 is disposed at a slight gap from the outercircumferential surface 36 b of the slider 36 that is sufficient toprevent contact.

An inner wall surface of the lower yoke 34 b that protrudes into theenclosure 33 is a facing surface 44. In the same way as the facingsurface 42 described above, the facing surface 44 is also disposedfacing the outer circumferential surface 36 b of the slider 36, and isdisposed so as to become a magnetic pole for the outer circumferentialsurface 36 b and the end surface 36 a of the slider 36.

That is, in the present embodiment, the facing surface 44 is also a“tooth part”.

The facing surface 44 is disposed at a slight gap from the outercircumferential surface 36 b of the slider 36 that is sufficient toprevent contact.

It should be noted that the width of the gap is the same as the width ofthe gap between the facing surface 42 and the outer circumferentialsurface 36 b of the slider 36.

It is possible to manufacture the solenoid 30 so that the gaps are thesame for the facing surfaces 42, 44 and have an extremely minute widthsince an accurate assembling of the components can be achieved duringthe manufacturing stage of the solenoid 30 by assembling the upper yoke34 a and the lower yoke 34 b with the bearing 40 as an alignment.

In the present embodiment, a groove 46 is formed in the outercircumferential surface 36 b of the slider 36 at a part corresponding tothe facing surface 42 of the upper yoke 34 a.

The groove 46 is formed so as to be concave in a direction away from thefacing surface 42 and is formed in a ring around the outer circumferenceof the slider 36.

The one end-side of the groove 46 (the side distant from the bearing 40)is positioned facing the facing surface 42 of the upper yoke 34 a as atooth part 48, and functions as a magnetic pole.

The formation position of the groove 46 shown here is such that thegroove 46 is formed at a position located a distance equal to the widthof the facing surface 42 displaced from the other end of the slider 36toward the one end. That is, the tooth part 48 is formed withsubstantially the same width as the width of the facing surface 42facing the tooth part 48.

A recess 49 formed with a larger diameter than other parts is formed atthe end of the bearing 40 on the upper yoke 34 a side so that an upperend edge part 45 (that is, an end part of the tooth part 48) of thegroove 46 on a side distant from the bearing 40 does not come intocontact within the range of possible movement of the slider 36.

It should be noted that the range of possible movement of the slider 36may be set so that the upper end edge part 45 (that is the end part ofthe tooth part 48) on the side of the groove 46 that is distant from thebearing 40 does not contact the bearing 40.

That is, as shown in FIG. 1, the range of possible movement of theslider 36 is designed so that the upper end edge 45 stops short of aposition x i.e. the end of bearing 40 when the slider has been pulled asfar as possible into the solenoid by attraction.

According to this construction, damage to the bearing 40 can beprevented, and in this case, the recess 49 does not need to be formed inthe bearing 40.

Next, the magnetic path of the solenoid of the present embodiment willbe described.

When a predetermined current flows through the excitation coil 32 of thesolenoid 30, a magnetic path b is produced as shown by the dotted line.It should be noted that the direction of the magnetic field of themagnetic path b shows merely an example. The magnetic path thatsurrounds the excitation coil 32 shown on the upper side in FIG. 1 hasbeen omitted from the drawing.

The magnetic path b is composed of a closed magnetic path that passesthrough the yoke 34 and the slider 36 in a circle.

That is, the magnetic path b passes through the lower yoke 34 b, throughthe air from an inner circumferential surface 44 a of the facing surface44 of the lower yoke 34 b into the slider 36 via the end surface 36 athe slider 36 (arrow D), inside the slider 36 along the axial direction,and reaches the facing surface 42 of the upper yoke 34 a. The magneticpath b passes from the outer circumferential surface 36 b of the slider36 through the air to an end surface 42 a of the facing surface 42(arrow E), and passes from the upper yoke 34 a to the lower yoke 34 b,thereby completing a circle.

The magnetic paths that are origin of the propulsion consist of themagnetic path from the tooth part 48 of the slider 36 via an inside ofthe groove 46 to an inner circumferential surface 42 b of the facingsurface 42 (the arrow F) and the magnetic path from the facing surface44 via the bearing 40 to the outer circumferential surface 36 b of theslider 36 (the arrow G).

In this way, by providing the groove 46 in the slider 36, a tooth partthat acts as a magnetic pole is formed in the slider 36, which assistsin the formation of magnetic paths that contribute to the propulsion.

In other words, since propulsion is determined by the change in thepermeance with respect to the moved amount of the slider (based on theexpression dP/dx mentioned above), by providing the groove 46 in theslider 36, when the slider 36 moves, the permeance can be changed inaccordance with the movement and therefore propulsion can be generated.

Second Embodiment

Next, a second embodiment where the formation positions of the grooveand the tooth parts differ to the first embodiment described above willbe described with reference to FIG. 2. It should be noted that somecomponents that are the same as in the embodiment described above havebeen designated the same reference numerals and description thereof hasbeen omitted.

In the present embodiment, the parameters n, m given in the patentclaims are set so that n=1 and m=0.

The yoke 54 includes an upper yoke 54 a and a lower yoke 54 b.

A groove 56 is formed in a facing surface 52 on an inner wall surface ofthe upper yoke 54 a that protrudes into the enclosure 33.

The groove 56 is formed so as to be concave in a direction away from theouter circumferential surface 36 b of the slider 36 and is formed in acircle around the inner circumference of the facing surface 52.

The respective ends of the groove 56 are formed as a tooth part 58 and atooth part 59. Both tooth parts 58, 59 are positioned opposite a grooveand a tooth part (described later) of the outer circumferential surface36 b of the slider 36 and function as magnetic poles.

The facing surface 52 of the upper yoke 54 a is disposed at a slight gapfrom the outer circumferential surface 36 b of the slider 36 that issufficient to prevent contact.

An inner wall surface side of the lower yoke 54 b that protrudes intothe enclosure 33 is a facing surface 55. In the same way as the facingsurface 52 described above, the facing surface 55 is also disposedfacing the outer circumferential surface 36 b of the slider 36, and isdisposed so as to be a magnetic pole for the outer circumferentialsurface 36 b and the end surface 36 a of the slider 36. That is, thefacing surface 55 is also a tooth part.

The facing surface 55 is disposed at a slight gap from the outercircumferential surface 36 b of the slider 36 that is sufficient toprevent contact.

It should be noted that two grooves 60 and 62 are formed in a part ofthe outer circumferential surface 36 b of the slider 36 that faces thefacing surface 42 of the upper yoke 34 a.

The grooves 60, 62 are formed so as to be concave in a direction awayfrom the facing surface 52 and are formed in circles around the outercircumference of the slider 36.

The one-end side of the groove 62 (the side that is distant from thebearing 40) is positioned facing the facing surface 52 of the upper yoke54 a as a tooth part 66 and functions as a magnetic pole.

A part sandwiched by the groove 60 and the groove 62 is also formed as atooth part 64 that functions as a magnetic pole.

That is, the present embodiment is characterized by the single groove 56and the two tooth parts 58, 59 being provided in the upper yoke 54 a andthe two grooves 60, 62 and the two tooth parts 64, 66 being provided atpositions of the slider 36 that face the upper yoke 54 a.

By increasing the number of tooth parts that act as magnetic poles inthis way compared to the first embodiment, a higher permeance isachieved than in the first embodiment, so that even higher propulsioncan be realized.

Third Embodiment

Next, a third embodiment where the formation positions of the toothparts differ to the first and second embodiments described above will bedescribed with reference to FIG. 3. It should be noted that somecomponents that are the same as in the embodiments described above havebeen designated the same reference numerals and description thereof hasbeen omitted.

In the present embodiment, the parameters n, m given in the patentclaims are set so that n=1 and m=1.

In the present embodiment, in addition to the construction of the secondembodiment, a groove 70 is formed in the facing surface 55 of the loweryoke 54 b and a tooth part 72 and a tooth part 74 that act as magneticpoles are provided at both ends of the groove 70.

A groove 76 is also formed in the outer circumferential surface 36 b ofthe slider 36 at a position facing the facing surface 55 of the loweryoke 54 b.

A tooth part 78 is provided on the other end-side of the groove. Thetooth part 78 is positioned facing the tooth part 72 of the facingsurface 55 of the lower yoke 54 b and functions as a magnetic pole.

By increasing the number of tooth parts that act as magnetic poles inthis way compared to the second embodiment, an even higher permeance isachieved than in the second embodiment, so that even higher propulsioncan be realized.

It should be noted that the formation positions of the grooves and thetooth parts are not limited to the respective embodiments describedabove, and the formation positions and numbers can be changed withinranges that satisfy the state disclosed in the patent claims.

In the embodiments described above, the respective grooves and toothparts have been illustrated as having rectangular cross-sectional forms.However, the cross-sectional forms of the grooves and tooth parts arenot limited to this, and may be trapezoidal. By making the formstrapezoidal, the magnitude of the propulsion can be made different towhen rectangular forms are used.

WORKING EXAMPLE

FIG. 4 shows the relationship between the stroke (amount ofdisplacement) of the slider of the solenoid of the second embodimentdescribed above and the generated propulsion. It should be noted that inthe present graph, the propulsion-displacement characteristics of theconventional solenoid shown in FIG. 7 have also been shown forcomparison purposes.

As shown in FIG. 4, by using the solenoid of the present invention, thepropulsion characteristics in the controlled range determined by theamount of current flowing through the excitation coil 32 can be madesubstantially flat, and on average compared to the conventionalsolenoid, at least double the propulsion can be obtained. For thisreason, a solenoid with extremely good controllability can be provided.

Various aspects of the present invention have been described above byway of favorable embodiments, but it should be obvious that the presentinvention is not limited to these embodiments and can be subjected tovarious modifications without departing from the spirit of the presentinvention.

EFFECT OF THE INVENTION

In the solenoid of the present invention, the body size can beminiaturized compared to the conventional art, the region where thepropulsion is stabilized can be widened, and the controllability can beimproved. In addition, higher propulsion can be obtained than before.

1. A solenoid comprising: an excitation coil; a slider disposed in acentral part of the excitation coil; and a yoke including a first yokepart that covers one end surface of the excitation coil and has a facingsurface that faces an outer circumferential surface of the slider, asecond yoke part that covers another end surface of the excitation coiland has a facing surface that faces the outer circumferential surface ofthe slider, and a linking part that links the first yoke and the secondyoke and covers an outer circumferential part of the coil, the yokeforming a closed magnetic path together with the slider, wherein abearing is sandwiched between the first yoke part and the second yokepart, is disposed on an outer circumference of the slider, and guidesthe slider in a movable state, the bearing being made of a nonmagneticbody, n (where n is a positive integer of 0 or higher) grooves, whichare provided so as to be concave around an inner circumference, and n+1tooth parts, which are adjacent to the grooves and function as magneticpoles, are provided in the facing surface of the first yoke part, m(where m is a positive integer of 0 or higher) grooves, which areprovided so as to be concave around an inner circumference and m+1 toothparts, which are adjacent to the grooves and function as magnetic poles,are provided in the facing surface of the second yoke part, n+1 grooves,which are provided so as to be concave around an outer circumference,and n+1 tooth parts, which are adjacent to the grooves and function asmagnetic poles, are provided in a surface of the slider that faces thefirst yoke part, and m grooves, which are provided so as to be concavearound an outer circumference, and m tooth parts, which are adjacent tothe grooves and function as magnetic poles, are provided in a surface ofthe slider that faces the second yoke part.
 2. A solenoid according toclaim 1, wherein the facing surfaces formed on the first yoke part andthe second yoke part have a same internal diameter.
 3. A solenoidaccording to claim 1, wherein the grooves and the tooth parts are formedso as to be rectangular or trapezoidal in cross-section.
 4. A solenoidaccording to claim 2, wherein the grooves and the tooth parts are formedso as to be rectangular or trapezoidal in cross-section.
 5. A solenoidaccording to claim 1, wherein a part, which is an upper end edge part ofthe groove provided in the slider and is located on a far side withrespect to the bearing in an axial direction, is formed at a positionthat does not contact the bearing in a range where the slider moves. 6.A solenoid according to claim 2, wherein a part, which is an upper endedge part of the groove provided in the slider and is located on a farside with respect to the bearing in an axial direction, is formed at aposition that does not contact the bearing in a range where the slidermoves.
 7. A solenoid according to claim 3, wherein a part, which is anupper end edge part of the groove provided in the slider and is locatedon a far side with respect to the bearing in an axial direction, isformed at a position that does not contact the bearing in a range wherethe slider moves.
 8. A solenoid according to claim 4, wherein a part,which is an upper end edge part of the groove provided in the slider andis located on a far side with respect to the bearing in an axialdirection, is formed at a position that does not contact the bearing ina range where the slider moves.
 9. A solenoid according to claim 1,wherein a recess is formed in the bearing so that a part, which is anupper end edge part of the groove provided in the slider and is locatedon a far side with respect to the bearing in an axial direction, doesnot contact the bearing in a range where the slider moves.
 10. Asolenoid according to claim 2, wherein a recess is formed in the bearingso that a part, which is an upper end edge part of the groove providedin the slider and is located on a far side with respect to the bearingin an axial direction, does not contact the bearing in a range where theslider moves.
 11. A solenoid according to claim 3, wherein a recess isformed in the bearing so that a part, which is an upper end edge part ofthe groove provided in the slider and is located on a far side withrespect to the bearing in an axial direction, does not contact thebearing in a range where the slider moves.
 12. A solenoid according toclaim 4, wherein a recess is formed in the bearing so that a part, whichis an upper end edge part of the groove provided in the slider and islocated on a far side with respect to the bearing in an axial direction,does not contact the bearing in a range where the slider moves.
 13. Asolenoid according to claim 5, wherein a recess is formed in the bearingso that a part, which is an upper end edge part of the groove providedin the slider and is located on a far side with respect to the bearingin an axial direction, does not contact the bearing in a range where theslider moves.
 14. A solenoid according to claim 6, wherein a recess isformed in the bearing so that a part, which is an upper end edge part ofthe groove provided in the slider and is located on a far side withrespect to the bearing in an axial direction, does not contact thebearing in a range where the slider moves.
 15. A solenoid according toclaim 7, wherein a recess is formed in the bearing so that a part, whichis an upper end edge part of the groove provided in the slider and islocated on a far side with respect to the bearing in an axial direction,does not contact the bearing in a range where the slider moves.
 16. Asolenoid according to claim 8, wherein a recess is formed in the bearingso that a part, which is an upper end edge part of the groove providedin the slider and is located on a far side with respect to the bearingin an axial direction, does not contact the bearing in a range where theslider moves.